1. Field of Invention
The invention relates to an antenna and, more particularly, to a planar multi-band antenna.
2. Related Art
Wireless transmission is widely used in electronic products. To satisfy the demand of the users, most electronic devices nowadays have wireless transmission functions. In the wireless transmission system, antenna is one of important elements for transmitting and receiving signals. Without antennas, the wireless transmission system cannot transmit and receive data. Therefore, the antenna is necessary in wireless transmission systems.
Planar Inverter-F antenna (PIFA) is a common antenna architecture nowadays. Such structure can be used to design a single-band antenna, a dual-band antenna and a multi-band antenna. FIG. 1 is a schematic diagram showing a conventional PIFA. Three antennas 11, 12 and 13 are PIFA, and they may have the same or different frequencies. An antenna for notebook computer applications shall be long and narrow, taking the antenna 11 as an example, in the long and narrow space, segments A1B1D1 and A1B1C1 are operated in a λ/4 mode. Since other high modes operate at higher frequencies (such as a 3λ/4 mode), or they are hard to be excited (such as a λ/2 and a λ mode), the PIFA architecture is hard to achieve a dual broadband antenna or a broadband antenna.